Field of the Invention
This invention relates to a control device for an internal combustion engine, and particularly to a control device for an internal combustion engine including port injection valves that inject fuel into an intake passage.
Description of the Background Art
Japanese Patent Laying-Open No. 2013-068127 discloses a control device to be applied to an internal combustion engine including a fuel pump and a fuel pressure sensor that detects a supply pressure of fuel to be supplied to port injection valves from the fuel pump. The control device outputs an amount of operation of the fuel pump in accordance with a detection value of the fuel pressure sensor.
This control device changes, for a diagnosis of the fuel pressure sensor, the amount of operation of the fuel pump in a direction of increasing the supply pressure, and determines the presence or absence of a failure in the fuel pressure sensor based on the detection value of the fuel pressure sensor at that time.
A failure diagnosis of the fuel pressure sensor is performed as follows. The drive duty of the fuel pump is increased to a diagnostic duty to thereby increase the fuel pressure to a valve opening pressure of the relief valve. If the fuel pressure sensor at that time has not detected a pressure around the valve opening pressure, it is determined that the fuel pressure sensor is in an abnormal state.
The control device described in the above-described document performs an abnormality diagnosis of the fuel pressure sensor when there is an increase in deviation in air-fuel ratio. It is, however, desirable to detect an abnormality in the fuel pressure sensor before the deviation in air-fuel ratio due to the abnormality in the fuel pressure sensor actually continues.
Further, although the control device described in the above-described document checks whether the fuel pressure sensor detects a pressure around the valve opening pressure of the relief valve, it is more preferred to check the performance of the fuel pressure sensor in further detail. For example, in order to check whether the detection value of the fuel pressure sensor changes, it is necessary to check detection values of the fuel pressure sensor at at least two pressures. This failure detection to check whether the detection value of the fuel pressure sensor has not become a fixed value is referred to as the “stuck detection”.
Although it is preferred to perform the stuck detection before the influence of an actual failure becomes serious, results of experiments conducted by the inventors of this application have shown that in order to complete the stuck detection at an early stage, it is necessary to sufficiently consider with what timing and what pressure conditions the stuck detection is to be performed.